3rd Grade · 3.MD.A.2

Liquid volume in 3rd grade

In 3rd grade math, liquid volume is the amount of liquid a container holds, measured in liters. Your child also measures mass, which is how heavy an object is, in grams and kilograms. At school, your child estimates these amounts, reads them on a beaker or a scale and uses them in one-step word problems.

What the standard says

The official Common Core wording, quoted exactly. The plain version follows.

3.MD.A.2 Measure and estimate liquid volumes and masses of objects using standard units of grams (g), kilograms (kg), and liters (l). Add, subtract, multiply, or divide to solve one-step word problems involving masses or volumes that are given in the same units, e.g., by using drawings (such as a beaker with a measurement scale) to represent the problem.

What it means, in plain words

Liquid volume tells how much liquid fits in a container. Liquid volume in 3rd grade is measured in liters, written L. Many large water bottles hold 1 liter. A cup holds less than 1 liter, and a bathtub holds many liters.

Mass is how heavy an object is. Light objects are measured in grams, written g: a paper clip has a mass of about 1 gram. Heavier objects are measured in kilograms, written kg: a full 1-liter bottle of water has a mass of about 1 kilogram. In 3rd grade, mass and volume are measured in these metric units, the units most of the world uses.

Your child reads liquid volume on a beaker, a clear container with marks up its side. Then your child adds, subtracts, multiplies or divides to solve one-step word problems with liters or with grams and kilograms. All the amounts in one problem use the same unit, so there is no changing from one unit to another yet.

Your child should be able to:

Choose grams or kilograms for an object and make a sensible estimate of its mass
Read the liquid volume on a beaker, even when the marks count by 2s or 5s
Solve one-step word problems with liters, grams or kilograms
Draw a beaker or a scale to show what a word problem says

Example

A fish tank holds 24 liters of water. A bucket holds 3 liters. How many full buckets of water fill the tank?

Each bucket adds 3 liters, so find how many 3s make 24.
$24 \div 3 = 8$
It takes 8 full buckets to fill the fish tank.

Example

A box of crayons has a mass of 350 grams. A book has a mass of 600 grams. How much more mass does the book have?

Both masses are in grams, so subtract.
$600 - 350 = 250$
The book has 250 grams more mass than the box of crayons.

Where children usually get stuck

The marks on a beaker go up by 2 liters. Your child reads water at the fourth mark as 4 liters.
The child counts marks as if each one were 1 liter and does not check the numbers written on the scale.
What helps. Before reading any amount, ask what each jump between two marks is worth. Then count the marks together by that number: 2, 4, 6, 8.
Your child says a tall, thin glass holds more water than a short, wide bowl, because the water looks higher.
Height is easy to see, so the child judges the amount by height alone. The width of a container matters just as much.
What helps. Fill the tall glass and pour the water into the bowl. Then pour it back, so your child sees that the amount stayed the same.
Your child says a watermelon has a mass of 5 grams.
Grams and kilograms are both new words, and the child has no feel yet for how light a gram is.
What helps. Hold a paper clip in one hand and a full 1-liter bottle of water in the other. One is about 1 gram and the other about 1 kilogram.

Try four practice questions

Real 3rd grade questions from our question bank, easiest first. Answer them right here, check each one, and see a worked solution for any question.

1Warm-up
Each of 4 identical beakers holds the amount of water shown below. Read the lowest point of the water's curved surface.
Drag tiles to build a multiplication equation that shows the total volume of water in all the beakers.
Tap or click a tile to drop it into the highlighted blank, or tap an empty blank first to choose a different one. Tap a filled blank to send its tile back.
×
=
4
9
8
7
2
6
Tap an item to place it in the next empty slot, or drag it to a specific slot. With a keyboard: select an item with Enter or Space, then select a slot to place it. Press Delete or Backspace on a slot to remove an item.
Show the answer and how to solve it
The total volume is $8$ liters. The equation $2 \times 4 = 8$ shows that $4$ beakers each holding $2$ liters add up to $8$ liters in all. The order of the two factors does not matter, so $4 \times 2 = 8$ is also correct.
1. 1Read the lowest point of the water's curved surface. It lines up with the $2$ -liter mark, so each beaker holds $2$ liters.
2. 2There are $4$ identical beakers, and each one holds the same $2$ liters of water. This is an equal-groups situation, so you can multiply to find the total.
3. 3Multiply the amount in one beaker by the number of beakers:
4. 4The total volume of water in all $4$ beakers is $8$ liters. The completed equation $2 \times 4 = 8$ shows the per-beaker amount, the number of beakers, and the total.
Common mistake. A common mistake is adding the values instead of multiplying — for example, choosing the tile $6$ as the total and writing $2 + 4 = 6$ . Adding gives the wrong total because the $4$ beakers each hold $2$ liters, which is an equal-groups situation that calls for multiplication, not addition.
The idea underneath. When you have equal groups of the same amount, multiplication finds the total: (number of groups) $\times$ (amount in each group) = total. The two factors can come in either order because multiplication is commutative.
2On level
Devontae says a bicycle has a mass of about 10 kilograms. Select the statement that best describes Devontae's estimate.
A
The estimate is reasonable for this object.
B
Changing only the unit makes the estimate reasonable.
C
The estimate is much too large. Changing only the unit will not fix it.
D
The estimate is much too small. Changing only the unit will not fix it.
Show the answer and how to solve it
The estimate is reasonable for this object. 10 kilograms fits the usual mass of a bicycle.
1. 1Devontae estimates the mass of a bicycle as 10 kilograms.
2. 2A typical bicycle has a mass of about 8 to 12 kilograms.
3. 310 kilograms is within that range.
4. 4Keep 10 and change only the unit to grams. 10 grams is too small for a bicycle.
5. 5The estimate is reasonable for this object. 10 kilograms fits the usual mass of a bicycle.
Common mistake. Keep the number and unit together. 10 kilograms is reasonable; 10 grams is too small.
The idea underneath. Compare an estimate with a familiar mass. Then keep the number and try the other unit. Read the whole choice.
3On level
Each bag of rice has a mass of 6 kg. What is the total mass of 8 bags?
kg
Show the answer and how to solve it
Answer. 48
The total mass is 48 kg, found by multiplying 6 kg per bag by 8 bags.
1. 1There are 8 bags of rice, and each bag has the same mass: 6 kg. This is an equal-groups situation, so the total can be found by multiplying.
2. 2Multiply the mass of one bag by the number of bags:
3. 3The total mass of 8 bags is 48 kg.
Common mistake. A common mistake is adding the two numbers instead of multiplying — that gives 14, not 48. When a problem describes equal groups, use multiplication.
The idea underneath. When a problem describes a number of equal groups, the total is the size of one group multiplied by the number of groups.
4Stretch
A farmer stored 456 kilograms of corn and 287 kilograms of wheat in a barn. How many kilograms of grain did the farmer store in all?
Which equation shows the correct solution?
A
$\displaystyle 456 - 287 = {}$
$\displaystyle 169$
B
$\displaystyle 456 + {}$
$\displaystyle 287 = {}$
$\displaystyle 753$
C
$\displaystyle 456 + {}$
$\displaystyle 287 = {}$
$\displaystyle 643$
D
$\displaystyle 456 + {}$
$\displaystyle 287 = {}$
$\displaystyle 743$
Show the answer and how to solve it
The correct equation is $456 + 287 = 743$ . The farmer stored $743$ kilograms of grain in all.
1. 1The farmer stored corn AND wheat in the barn. The phrase 'in all' tells you to combine the two amounts — that means you add.
2. 2Ones: $6 + 7 = 13$ . Regroup $10$ ones as $1$ ten. Keep $3$ ones and add the $1$ ten in the tens column.
3. 3Tens: $5 + 8 + 1 = 14$ . Regroup $10$ tens as $1$ hundred. Keep $4$ tens and add the $1$ hundred in the hundreds column.
4. 4Hundreds: $4 + 2 + 1 = 7$ . Keep $7$ hundreds.
5. 5The farmer stored $743$ kilograms of grain in all.
Common mistake. Do not leave out the regrouped $1$ hundred. It is worth $100$ , so leaving it out gives $643$ instead of $743$ .
The idea underneath. Regrouping keeps the same amount: $10$ ones become $1$ ten, and $10$ tens become $1$ hundred.